A solar cell is a core element of solar-light power generation, which directly transforms solar light into electricity, and it may be basically considered as a diode having a p-n junction. Solar light is transformed into electricity by a solar cell as follows. If solar light is incident to a p-n junction of a solar cell, an electron-hole pair is generated, and due to the electric field, electrons move to an n layer and holes move to a p layer, thereby generating photoelectromotive force between the p-n junctions. In this way, if a load or system is connected to both terminals of the solar cell, an electric power may flow to generate power.
A general solar cell is configured to have a front surface and a back electrode respectively at front and back surfaces of the solar cell. Since the front electrode is provided to the front surface which is a light-receiving surface, the light-receiving area decreases as much as the area of the front electrode. In order to solve the decrease of the light-receiving area, a back electrode-type solar cell has been proposed. The back electrode-type solar cell maximizes the light-receiving area of the front surface of the solar cell by providing a (+) electrode and a (−) electrode on a back surface of the solar cell.
FIG. 1 is a cross-sectional view showing a back electrode-type solar cell proposed in U.S. Pat. No. 7,339,110. Referring to FIG. 1, a p+ region where p-type impurity ions are implanted and a n+ region where n-type impurity ions are implanted by thermal diffusion are provided at the back surface of a silicon substrate, and interdigitated metal electrodes 50, 52 are provided on the p+ region and the n+ region.
In a method for manufacturing a back electrode-type solar cell disclosed in U.S. Pat. No. 7,339,110, thermal diffusion processes are respectively performed to form a p+ region and an n+ region, and an oxide film generated by each thermal diffusion process should be removed. When the thermal diffusion process is performed to form the n+ region, in order to define the n+ region, a process of selectively patterning an oxide film generated when the p+ region is formed is added.
As described above, in the conventional method for manufacturing a back electrode-type solar cell, two thermal diffusion processes must be performed, and at least four photolithography processes and etching processes are required for patterning oxide films and etching masks, resulting in very complicated processes.